A user may report if the Motherboard is replaced on their Optiplex 790, 990 or Precision T1600 that it does not have the Chipset Heatsink or Thermal Sensor installed.
The system may report an error during startup that the Thermal Sensor is not installed.

Resolution

These Motherboards were formally modified to eliminate both parts as of November 2011. The exclusion of these parts will not affect the operation of the system.

The BIOS was modified in a later revision to resolve any issues which may occur after a replacement Motherboard is installed.
Please refer to the Dell Support Site and download the latest version of BIOS for your system.